The present invention relates to a method and an apparatus for modifying a variable, more particularly to a method and an apparatus for setting a variable of an electronic instrument to a desired value.
When operating an electronic instrument, it is often required to set various parameters of the instrument, such as voltage, current, frequency and position of a point or cursor, etc. Interfacing devices, such as a rotary knob, mouse, key and/or button, are often used to assist setting these instrument variables.
In some cases of adjustment of a variable X, it is important that the variable X not pass beyond a given reference value Vr. FIG. 1 shows an example of a prior art method for setting a variable X, a voltage, to a desired value Vr, 0 volts. An alternative example could be setting the value of the variable X without letting the value drop below 0 volts. Although an operator could modify the value of the variable X by 0.001V or less by careful operation of the interface device, it is possible that the operator will operate the interface device roughly, such that the variable X would decrease at the rate of 0.1V per operation of the interface device. Therefore the operator could accidentally adjust the value of the variable X below 0V. To avoid dropping below 0V, the operator must use greater care in operating the interface device as the variable X approaches the desired value Vr. Therefore, careless operation of the interface device is unacceptable.
FIG. 2 shows a display waveform W1 and two vertical line cursors C1 and C2 which can be moved freely under operator control on the display in the horizontal direction. FIG. 3 shows a waveform W2 and two point cursors C3 and C4 which can be moved freely on the waveform W2. In the case of a waveform generator, the two cursors could be used to specify a region of one waveform within which to substitute another waveform to generate a new waveform signal. The two cursors could also be used for indicating where to insert markers on the waveform. In the case of an oscilloscope, the cursors could be used for measuring a waveform parameter, such as a time difference and/or a voltage difference between the two cursors.
It is known to simultaneously display two cursors on the display and independently control them while editing waveforms or making waveform measurements. For some critical applications for editing a waveform or making waveform measurements, it may be required that the cursors be accurately superimposed on top of one another. If an operator is carelessly operating the knob or other interface device for moving the first cursor C1 (or C3) toward the second cursor C2 (or C4), then as the second cursor approaches the first cursor, the operator could accidentally cause the second cursor to pass over the first cursor.
Therefore, it is desired to provide a method and an apparatus for setting a variable, such as voltage or current, or the position of a cursor, to a desired value via operation of an interface device, wherein the method and apparatus are tolerant of somewhat careless operation of the interface device. It is further desired to provide a method and an apparatus for adjusting a plurality of variables to the same value via control of the interface device, of which the method and apparatus are again tolerant of somewhat careless operation of the interface device and provide an operator a means to easily confirm the adjustments.